Mendel then crossed a pure & a hybrid from his F2 generation; known as an F2 or test cross

Trait – Plant Height

Alleles – T tall, t short

F2 cross TT x Tt

F2 cross tt x Tt

T

t

T

t

T

TT

Tt

t

Tt

tt

T

TT

Tt

t

Tt

tt

genotype – TT, Tt

genotype – tt, Tt

phenotype – Tall

phenotype – Tall & short

genotypic ratio– 1:1

genotypic ratio– 1:1

phenotypic ratio– all alike

phenotypic ratio– 1:1

50% (1/2) of the offspring in a test cross showed the same genotype of one parent & the other 50% showed the genotype of the other parent; always a 1:1 ratio

Problems:Work the P1, F1, and both F2 crosses for all of the other pea plant traits & be sure to include genotypes, phenotypes, genotypic & phenotypic ratios.

Mendel also crossed plants that differed in two characteristics (Dihybrid Crosses)
such as seed shape & seed color

In the P1 cross, RRYY x rryy, all of the F1 offspring showed only the dominant form for both traits; all hybrids, RrYy

Traits: Seed Shape & Seed Color

Alleles: R round Y yellow
r wrinkled y green

P1 Cross: RRYY x r r yy

ry

Genotype:

RrYy

RY

RrYy

Phenotype:

Round yellow seed

Genotypic ratio:

All alike

Phenotypic ratio:

All Alike

When Mendel crossed 2 hybrid plants (F1 cross), he got the following results

Traits: Seed Shape & Seed Color

Alleles: R round Y yellow
r wrinkled y green

F1 Cross: RrYy x RrYy

RY

Ry

rY

ry

RY

RRYY

RRYy

RrYY

RrYy

Ry

RRYy

RRyy

RrYy

Rryy

rY

RrYY

RrYy

r rYY

r rYy

ry

RrYy

Rryy

r rYy

r ryy

Genotypes

Genotypic Ratios

Phenotypes

Phenotypic Ratios

RRYY

1

Round yellow seed

9

RRYy

2

RrYY

2

RrYy

4

RRyy

1

Round green seed

3

Rryy

2

r rYY

1

Wrinkled yellow seed

3

r rYy

2

r ryy

1

Wrinkled green seed

1

Problems:Choose two other pea plant traits and work the P1 and F1 dihybrid crosses. Be sure to show the trait, alleles, genotypes, phenotypes, and all ratios.

Results of Mendel’s Experiments:

Inheritable factors or genesare responsible for all heritable characteristics

Phenotype is based on Genotype

Eachtrait is based on two genes,one from the mother and the other from the father

True-breedingindividuals are homozygous ( both alleles) are the same

Law of Dominance states that when different alleles for a characteristic are inherited (heterozygous), the trait of only one (the dominant one) will be expressed. The recessive trait’s phenotype only appears in true-breeding (homozygous) individuals

Trait: Pod Color

Genotypes:

Phenotype:

GG

Green Pod

Gg

Green Pod

gg

Yellow Pod

Law of Segregation states that each genetic trait is produced by a pair of alleles which separate (segregate) during reproduction

Rr

R

r

Law of Independent Assortment states that each factor (gene) is distributed (assorted) randomly and independently ofone another in the formation of gametes

RrYy

RY

Ry

rY

ry

Other Patterns of Inheritance:

Incomplete dominance occurs in the heterozygous or hybrid genotype where the 2 alleles blend to give a different phenotype